1. Field of the Invention
This invention relates to a cooling control system and a cooling control method for cooling an engine of, for example, a vehicle, more particularly, to a cooling control system and method capable of enhancing the responsibility of a temperature control with respect to cooling medium circulated in the engine and improving the control precision.
2. Description of the Related Art
In an engine used in a vehicle or the like, a water cooling type cooling device using a radiator is generally used for cooling the engine.
In this type of the cooling device, a thermostat is used in order to control temperature of the cooling water. When the temperature of the cooling water is lower than a predetermined temperature, the cooling water is circulated in a bypass passage so as not to flow into the radiator with the action of the thermostat.
FIG. 29 shows the above structure, in which numeral 1 is an engine composed of a cylinder block 1a and a cylinder head 1b, and a fluid conduit illustrated with arrow c is formed in the cylinder block 1a and the cylinder head 1b of the engine 1.
Numeral 2 is a heat exchanger, namely a radiator. A fluid conduit 2c is formed in the radiator 2 as well-known, and a cooling-water inlet portion 2a and a cooling-water outlet portion 2b of the radiator 2 are connected to a cooling-water conduit 3 circulating the cooling water between the engine 1 and the radiator 2.
The cooling-water conduit 3 is composed of an outflow-side cooling-water conduit 3a linking from an outflow portion id of the cooling water, placed in the upper portion of the engine, to the inflow portion 2a of the cooling water placed in the upper portion of the radiator 2; an inflow-side cooling-water conduit 3b linking from the outflow portion 2b of the cooling water, placed in the lower portion of the radiator 2, to an inflow portion 1e of the cooling water placed in the lower portion of the engine 1; and a bypass conduit 3c connecting the conduits 3a and 3b to each other.
In a branch portion between the outflow-side cooling-water conduit 3a and the bypass conduit 3c in the cooling-water conduit 3, a thermostat 4 is disposed. The thermostat 4 is provided therein with a thermal expansive body (e.g. wax) expanding and shrinking with changing of temperature of the cooling water. When the cooling-water temperature is high (e.g. over 80.degree. C.), the valve is opened by the expansion of the thermal expansive body so that the cooling water flowing from the outflow portion 1d of the engine 1 flows through the outflow-side cooling-water conduit 3a into the radiator 2. The cooling water cooled in the radiator 2 and dissipating heat is operated to flow from the outflow portion 2b through the inflow-side cooling-water conduit 3b, and through the inflow portion 1e of the engine 1 into the engine 1.
When the temperature of the cooling water is low, the valve of the thermostat 4 is closed by the shrinkage of the thermal expansive body, so that the cooling water flowing from the outflow portion 1d of the engine 1 flows through the bypass conduit 3c, and through the inflow portion 1e of the engine into cooling pipes c of the engine 1.
In FIG. 29, numeral 5 is a water pump disposed in the inflow portion 1e of the engine 1, of which the rotating shaft is rotated by the rotation of a crank-shaft (not shown) of the engine 1, so that the cooling water is forcibly circulated. Numeral 6 is a fan unit for forcibly blowing cooled air into the radiator 2, and composed of a cooling fan 6a and a fan motor 6b rotationally driving the cooling fan 6a.
The valve opening and the valve closing actions by the thermostat are determined by the temperature of the cooling water, and also by the expansion and shrinkage of the thermal expansive body such as wax, therefore the temperature in the valve opening and the temperature in the valve closing are not constant. The thermal expansive body such as wax takes some time to operate the valve after receiving the changing of the temperature of the cooling water until. Especially, the responsibility during the decrease of the temperature is inferior as compared with that during the increase of the temperature, that is to say it has hysteresis properties. As a result, there is a technical disadvantage in which the cooling water is not easily adjusted to be in a constant temperature required.
It is proposed that the flow of the cooling water is electrically controlled not to harness the actions of opening and closing valve by the thermal expansive body such as wax.
This is, for example, the control of a rotational angle of a butterfly valve using a stepping motor. Omitting the thermostat 4 shown in FIG. 29, a valve unit 7 provided with the butterfly valve instead of the thermostat 4 is disposed in the outflow-side cooling-water conduit 3a as illustrated with a long dashed line in FIG. 29.
FIG. 30 shows an example of the above valve unit 7, in which a circular plane shaped butterfly valve 7a is supported in the cooling-water conduit 3a to be rotated by a shaft 7b. A worm wheel 7c is attached on an end of the shaft 7b, and a worm 7e inserted in a rotational drive shaft of a motor 7d is engaged with the worm wheel 7c.
The motor 7 is supplied with the operation current for rotating the drive shaft thereof in the forward and reverse directions by a control unit (ECU) controlling the operation condition of the overall engine. Therefore, when the current for rotating the drive shaft in the forward direction is passed into the motor 7d by the action of the ECU, the shaft 7b of the butterfly valve 7a is rotated in one direction by a well-known decelerating action produced by the worm 7e and the worm wheel 7c, whereby the plane direction of the butterfly valve 7a is rotated in the same direction as the flowing direction of the cooling-water conduit 3a, resulting in the valve opening state.
On the other hand, when the current for rotating the drive shaft in the reverse direction is passed into the motor 7d by the action of ECU, the shaft 7b of the butterfly valve 7a is rotated in the other direction, whereby the plane direction of the butterfly valve 7a is rotated in a direction perpendicular to the flowing direction of the cooling-water conduit 3a, resulting in the valve closing state.
The ECU receives information such as the temperature of the cooling water in the engine, and controls the temperature of the cooling water by controlling the aforementioned motor with the use of the above information.
In addition, in response to a control signal from the control unit (ECU) fetching various operational parameters which are detected from the engine, a stepping motor (not shown) rotating the butterfly valve is driven so as to control the flow of the cooling water flowing toward the radiator.
In the cooling control system using the butterfly valve as described thus far, a temperature detecting element such as a thermistor (not shown) is disposed in a part of the pipes for the cooling water in the engine 1, and the motor 7d is driven responsive to the temperature of the cooling water detected by the temperature detecting element.
According to the structure as described above, the effects of the hysteresis properties seen in the former example using the thermostat including the thermal expansive body is decreased somewhat.
After the temperature detecting element senses the changing of the temperature of the cooling water, however, the ECU controls an angle of the valve on the basis of the sensed changing, that is to say it is a follow-up control. In consequence, in this point both examples are the same.
Even the cooling control system using the butterfly valve in the latter example cannot escape having a hunting phenomenon which is the temperature of the cooling water is changed around a specific temperature Tc at all times, resulting in the difficulty of the control with stability and high precision.
Generally, when an engine for a vehicle is driven in a high temperature state before overheating, fuel economy is enhanced and the generation of a poisonous gas is reduced.
When the aforementioned hunting occurs, in order to avoid the worst state of the overheating of the engine, the aforementioned temperature Tc of the cooling water should be adjusted to be lower, thereby creating a technical disadvantage of sacrificing fuel economy.
Where an actuator to rotate the aforementioned butterfly valve is concerned, for example, the stepping motor is provided therein as described hereinbefore, and driven by the pulse control signal caused by ECU, thereby rotating the butterfly valve.
The maximum rotational speed (rpm/min) of the aforementioned type of the stepping motor is extremely lower on the action thereof than that of a direct-current motor as is well-known. Therefore, when it is structured to obtain predetermined rotation torque using the aforementioned worm gear or another decelerating gear, and to afford the appropriate rotational speed to the butterfly valve, the motor itself is inevitably required to have high torque, resulting in a technical disadvantage in that the overall actuator is larger in size.
Moreover, for example, upon any failure occurring in the motor or damage of the aforementioned decelerating gear, the operation of opening and closing the butterfly valve results in an impossibility. For example, when the above failure or damage occurs in a state that the butterfly valve is closed or is nearly closed at a half open angle, the engine is cooled insufficiently, thereby having a technical disadvantage in that the engine is overheated without being noticed by a driver.
The present invention is performed in order to resolve the technical disadvantages described thus far. It is an object of the present invention to provide a cooling control system and a cooling control method having the improved control precision in which temperature is conducted in a state that the changing of temperatures of the cooling water is forecast, and the aforementioned hunting does not occur.
It is another object of the present invention to provide a cooling control system capable of exploiting a fail-safe function and previously avoiding disadvantages such as the overheat of an engine, controlled by damaging a part of a drive device of a flow control valve or the like.
In the structure in which the valve unit 7 is controlled by the stepping motor after receiving the control signal from the ECU as described above, there may be cases where an opening sensor for detecting the degree of valve opening (not shown) as well as the stepping motor rotationally driving the butterfly valve is needed. This needs adoption of a complicated control system, for example, the stepping motor is driven by returning the information of the opening sensor to the ECU, resulting in high costs.
The present invention is carried out in order to resolve the aforementioned technical disadvantage, and is characterized in that the degree of butterfly-valve opening is controlled with a thermo-element enclosing a thermal expansive body such as wax, and the thermal-element is forcibly operated by a heater to respond thermally. Therefore, it is an object of the present invention to provide a cooling control system capable of improving the responsibility of a temperature control for cooling water and the control precision at small cost.